Electric machinery, e.g., motor, has a rotor and a stator. The stator includes a stator core having tooth sections, and magnet wires are wound on the tooth sections, which is covered with an insulator, so as to form stator coils. To improve performance of the motor, a large volume of the magnet wires are wound in gaps, each of which is formed between the adjacent tooth sections, so as to highly improve space factor of the coils.
Conventionally, nozzles of a wire coiling machine are inserted into the gaps formed between the adjacent tooth sections, in a direction of stacking stator cores, so as to wind magnet wires on the tooth sections, so the magnet wires cannot be wound in the gaps, in which the nozzles are inserted and moved. For example, in FIG. 12A, coils 54 are respectively wound on tooth sections 52a and 52b of a stator core 51, which are covered with an insulator 53. When the coils 54 are wound, a nozzle of a wire coiling machine (not shown) is inserted into a gap 55, in a direction of stacking stator cores (a direction parallel to an axial direction of the stator core), so as to wind a magnet wire on the tooth sections 52a and 52b. 
To increase space factor by regular-winding the coils with preventing inferior winding, as shown in FIG. 12B, partition walls 53a, which correspond to middle parts of tooth sections 52a and 52b, are projected from an insulator 53 covering the tooth sections 52a and 52b, so each of the tooth sections 52a and 52b is divided into an inner part and an outer part. A magnet wire is wound on the inner parts and the outer parts to form inner coils 54a and outer coils 54b (see Japanese Laid-open Patent Publication No. 11-27886).
There is another method of forming stator coils, in which motor efficiency is improved by eliminating spaces for inserting nozzles (needles) of a wire coiling machine. For example, in case of forming stator coils on a circular stator core of a three-phase/12-slot/inner rotor-type motor, each of U-phase coils, V-phase coils and W-phase coils are radially formed in two slots, each of which is a space formed around each of tooth sections, by using three needles for feeding magnet wires. The needles are inserted into the slots, each of which is formed around each of the tooth sections, reciprocated in a direction of stacking stator cores and moved in the radial direction of the stator core so as to wind the magnet wires of a first layer in the slots of each phase. Then, the stator is turned 90 degrees, and the magnet wires are wound, as well. Further, the turning action and the winding action are repeated. For example, in case of winding the U-phase coils, coils U1-U4 are wound by repeating the above described actions.
Next, the needle is inserted into a radially-intermediate position of the coil U4, and then a coil U5 of a second layer is lap-wound, in an outer part, from the radially-intermediate position toward an outer end. Further, the stator is turned 180 degrees, and a coil U6 of the second layer is lap-wound, on the outer circumference of the coil U2, in the outer part, from a radially-intermediate position toward an outer end, as well as the coil U5.
Next, the needle is inserted into a radially-inner part of the slot, and a coil U7 of the second layer is lap-wound, on the coil U3 of the first layer, in an inner part, until reaching the radially-intermediate position. Further, the stator is turned 180 degrees, and a coil U8 of the second layer is lap-wound, on the outer circumference of the coil U1, in the inner part from the radially-intermediate position.
As described above, the coils U1-U4 and the coils U5-U8 are zigzag-wound, on the stator core, in the circumferential direction, so that the coils can be wound in spaces for inserting the nozzles (see Japanese Laid-open Patent Publication No. 2001-54265).
Further, another method of regular-winding coils has been invented (see Japanese Laid-open Patent Publication No. 2008-92654). In the method, the coils can be easily and high-densely wound on tooth sections of a dividable core, which are covered with an insulator, by a wire coiling machine.
After winding the coils 54 of FIG. 12A on the tooth sections 52a, 52b, etc. or after winding the coils 54a and 54b of FIG. 12B on the tooth sections 52a, 52b, etc. each of which is divided by the partition wall 53b, as described in Japanese Laid-open Patent Publication No. 11-27886, spaces S1 and S2 in each of the gaps 55, which are formed for inserting and moving the nozzle, become dead spaces S (see an enlarged view of FIG. 12C). Note that, in case that the coils 54a of inner parts and the coils 54b of outer parts are regular-wound on the tooth sections covered with the insulator having no partition walls as shown in FIGS. 12D and 12E, number of winding the magnet wires can be greater than that of the case shown in FIG. 12B. For example, in FIG. 12B, the magnet wire having a diameter of φ1.5 is multiple-wound to correspond to φ2.1 (wire diameter), total number of turn per tooth section of the coil 54a of the inner part is 192 turns (T), and number of turn of the coil 54b of the outer part is 168 T. On the other hand, in FIG. 12E, the numbers (T) are increased. Namely, the number of the coil 54a of the inner part is 216 T, and the number of the coil 54b of the outer part is 204 T. However, the spaces for moving the nozzles (the dead spaces S) must be formed in each of the gaps 55.
Especially, to apply large current at low voltage, the diameter of the magnet wires must be increased. If the diameter of the magnet wires is increased, it is difficult to regular-wind the coils. Further, if the gaps of the stator core are enlarged, it is difficult to downsize the motor.
In the method disclosed in Japanese Laid-open Patent Publication No. 2001-54265, if no supporting means are provided in the radially inner parts and radially outer parts, inferior winding will occur when the coils U5-U8 of the second layer are lap-wound on the coils U1-U4 of the first layer. So, the regular winding cannot be performed, and space factor must be lowered.
In the method disclosed in Japanese Laid-open Patent Publication No. 2001-54265, the dividable core is used, so the coils can be easily wound, but production steps and a production cost must be increased. Further, magnetic loss occurs at connection parts between divided core pieces, so performance of the motor must be lowered.